American Science and Engineering, Inc., proposes to develop a high resolution, low intensity X-ray computer tomography (CT) scanner suitable for the study of small laboratory animals such as mice, rats, and hamsters. Such a scanner could be used for the diagnosis of early tumors in rodents serving for the safety evaluation of various substances in carcinogenesis bioassays. This could greatly reduce the time required (and hence the cost) of such bioassays. Such a scanner could also be used for the noninvasive continuous measurement of tumor regression under chemotherapy in small rodents, as well as for the general diagnostic radiology of these animals. The proposed research consists of the construction of a laboratory "breadboard" model of a CT scanner having sufficient spatial resolution (0.05 mm) and sufficient contrast sensitivity for diagnostic radiology of small laboratory animals. We will then establish the appropriate conditions to achieve optimal images with the minimum effective X-ray dose. In a companion study, our collaborators, Bio-Research Consultants, Inc., will develop and validate the techniques required to apply the high resolution, low intensity CT scanner to carcinogenesis bioassays. If the results of this research are favorable, AS&E will develop and market a high reolution, low intensity CT scanner for laboratory animals. This will facilitate the conduct of studies intended to detect cancer causing substances.